Java如何用ObjectInputStream阅读
Java如何用ObjectInputStream阅读
提问于 2019-06-07 19:07:20
这是我第一次使用套接字，为了更好地了解发生了什么，我决定构建一个可以支持多个用户的客户端服务器聊天应用程序。
起初，我使用DataInputStream / DataOutputStream进行通信，一切工作正常。但我想换成ObjectStream，这就是问题所在。一旦我用ObjectInputStream / ObjectOutputStream替换了所有的DataInputStream / DataOutputStream，我就不能再打印检索到的数据。
这是我之前使用的代码，它是有效的(DataStream)：
服务器：
try {
DataInputStream in = new DataInputStream(socket.getInputStream());
DataOutputStream out = new DataOutputStream(socket.getOutputStream());
out.writeUTF("HI FROM SERVER");
while (!socket.isClosed()) {
try {
if (in.available() > 0) {
String input = in.readUTF();
for (ClientThread thatClient : server.getClients()){
DataOutputStream outputParticularClient = new DataOutputStream(thatClient.getSocket().getOutputStream());
outputParticularClient.writeUTF(input + " GOT FROM SERVER");
}
}
} catch (IOException e) {
e.printStackTrace();
}
}
} catch (IOException e) {
e.printStackTrace();
}客户端：
try {
socket = new Socket("localhost", portNumber);
DataInputStream in = new DataInputStream(socket.getInputStream());
new Thread(()->{
while(!socket.isClosed()){
try {
if (in.available() > 0){
String input = in.readUTF();
System.out.println(getUserName() + " > " + input);
}
} catch (IOException e) {
e.printStackTrace();
}
}
}).start();
} catch (IOException e) {
e.printStackTrace();
}这就是我尝试用ObjectStream实现同样的想法的方法：
服务器：
try {
ObjectInputStream in = new ObjectInputStream(socket.getInputStream());
ObjectOutputStream out = new ObjectOutputStream(socket.getOutputStream());
while (!socket.isClosed()) {
try {
if (in.available() > 0) {
Message input;
try {
input = (Message)in.readObject();
if (input.equals(null)){
System.err.println("SERVER RETRIEVED NULL OBJECT");
}
for (ClientThread thatClient : server.getClients()){
ObjectOutputStream outputParticularClient = new ObjectOutputStream(thatClient.getSocket().getOutputStream());
outputParticularClient.writeObject(input);
}
} catch (ClassNotFoundException e) {
e.printStackTrace();
}
}
} catch (IOException e) {
e.printStackTrace();
}
}
} catch (IOException e) {
e.printStackTrace();
}客户端：
try {
socket = new Socket(getHost(), portNumber);
ObjectInputStream in = new ObjectInputStream(socket.getInputStream());
new Thread(()->{
while(!socket.isClosed()){
try {
if (in.available() > 0){
Message input = null;
try {
input = (Message)in.readObject();
if (input.equals(null)){
System.err.println("CLIENT RETRIEVED NULL OBJECT");
}
System.out.println("CLIENT " + input.toString());
} catch (ClassNotFoundException e) {
e.printStackTrace();
}
}
} catch (IOException e) {
e.printStackTrace();
}
}
}).start();
} catch (IOException e) {
e.printStackTrace();
}我觉得这与if语句if (in.available() > 0)有关，但我不能确切地说出发生了什么。
回答 1
Stack Overflow用户
发布于 2019-06-08 00:25:32
available()的作用可能与您想象的不同，而且它在生产代码中几乎没有用处(对于ObjectInputStream来说尤其如此)。您没有收到任何数据的原因实际上是，正如您已经怀疑的那样，in.available()总是返回0。
正如注释中所指出的，StreamCorruptedException是由于写入已使用ObjectOutputStream的另一个实例写入的现有ObjectInputStream而导致的。请参阅答案StreamCorruptedException: invalid type code: AC以获得更多解释。
下面是一些快捷的示例代码，其中包含一个服务器回显来自两个客户端的消息。它不是干净的，但它可能会让你知道如何处理你的问题：
public class SO56493162 {
private static final class Message implements Serializable {
private static final long serialVersionUID = 1L;
private static int cnt = 0;
private final int id;
public Message(int id) {
++cnt;
this.id = id;
}
public String toString() {
return "Msg from " + id + " : " + cnt;
}
}
private static final class Client implements Runnable {
private InetSocketAddress addr = null;
private int id = -1;
Client(InetSocketAddress addr, int id) {
this.addr = addr;
this.id = id;
}
public void run() {
int timeout = 3000;
Socket s = null;
try {
s = new Socket();
s.connect(addr, timeout);
ObjectOutputStream oos = new ObjectOutputStream(s.getOutputStream());
ObjectInputStream ois = new ObjectInputStream(s.getInputStream());
System.out.println("Client " + id + " connected");
while (true) {
Thread.sleep(new Random().nextInt(2000));
Message hello = new Message(id);
oos.writeObject(hello);
oos.flush();
Message reply = (Message) ois.readObject();
System.out.println("Reply: " + reply.toString());
}
} catch (Exception e) {
e.printStackTrace();
} finally {
try {
s.close();
} catch (Exception ignore) {
}
}
}
}
private static final class Server implements Runnable {
private ServerSocket sock = null;
Server(ServerSocket sock) throws IOException {
this.sock = sock;
}
public void run() {
System.out.println("starting server");
try {
while (true) {
final Socket client = sock.accept();
System.out.println("connection accepted");
Thread t = new Thread(new Runnable() {
@Override
public void run() {
try {
ObjectInputStream ois = new ObjectInputStream(client.getInputStream());
ObjectOutputStream oos = new ObjectOutputStream(client.getOutputStream());
while (!client.isClosed()) {
try {
Message input = (Message) ois.readObject();
oos.writeObject(input);
oos.flush();
} catch (EOFException eof) {
System.err.println("EOF!");
client.close();
}
}
} catch (Exception e) {
e.printStackTrace();
}
}
});
t.setDaemon(true);
t.start();
}
} catch (Exception e) {
e.printStackTrace();
}
}
}
public static void main(String args[]) throws IOException, InterruptedException {
final int port = 9876;
Thread ts = new Thread(new Runnable() {
@Override
public void run() {
try {
new Server(new ServerSocket(port)).run();
} catch (Exception e) {
e.printStackTrace();
}
}
});
ts.setDaemon(true);
ts.start();
InetSocketAddress addr = new InetSocketAddress("localhost", port);
for (int i = 0; i < 2; ++i) {
Client cl = new Client(addr, i);
Thread tc = new Thread(cl);
tc.setDaemon(true);
tc.start();
}
Thread.sleep(10000);
System.err.println("done");
}
}页面原文内容由Stack Overflow提供。腾讯云小微IT领域专用引擎提供翻译支持
原文链接：
https://stackoverflow.com/questions/56493162
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